1. Field of the Invention
The present invention relates to a Group III nitride semiconductor light-emitting device which suppresses an increase in driving voltage and which exhibits improved emission performance.
2. Background Art
Hitherto, various known Group III nitride semiconductor light-emitting devices are known, and some of them are disclosed in Japanese Patent Application Laid-Open (kokai) No. 2008-103711. Japanese Patent Application Laid-Open (kokai) No. 2008-103711 discloses a Group III nitride semiconductor light-emitting device including an active layer having a structure in which the closer to an n-type contact layer, the larger a bandgap energy of an InGaN well layer; the closer to an n-type contact layer, the smaller the thickness of a well layer; and the closer to an n-type contact layer, the larger a bandgap energy of an InGaN barrier layer. This structure eliminates the nonuniformity of emission wavelength.
Moreover, Japanese Patent Application Laid-Open (kokai) No. 2009-152552 discloses a Group III nitride semiconductor light-emitting device including an active layer having a structure in which the thickness of a barrier layer is gradually increased as getting closer to a p-type layer to suppress overflow of carriers.
Further, Japanese Patent Application Laid-Open (kokai) No. 2003-273473 discloses a Group III nitride semiconductor light-emitting device including an active layer having a structure, the active layer comprising three layers of a barrier layer, a well layer, and a barrier layer, in which a bandgap energy of a barrier layer on the n-type layer side is larger than that of a barrier layer on the p-type layer side, and the thickness of a barrier layer on the n-type layer side is smaller than that of a barrier layer on the p-type layer side.
However, even in the Group III nitride semiconductor light-emitting device having the above structure, emission performance is required to be further improved. In the active layer of MQW (Multiple Quantum Well) structure, the electron diffusion length is larger than the hole diffusion length. Therefore, in the MQW structure, electrons injected from the n-type cladding layer to the active layer reaches the p-type cladding layer, and confined in the active layer by the barrier. As a result, more electrons are captured in the well layer closer to the p-type cladding layer. That is, the electron density distribution in the well layer of the active layer increases as getting closer to the p-type cladding layer. Thus, holes injected from the p-type cladding layer to the active layer are more recombined with the electrons confined in the well layer having a high electron density closer to the p-type cladding layer.
This leads to a problem that the emission region in the active layer is concentrated closer to the p-type cladding layer, causing a decrease in the total light output and the emission performance of the light-emitting device.